Firefighters experienced "heavy smoke conditions" when they responded to a fire aboard a Boeing 787 Dreamliner two months ago in Boston, portraying the incident as more serious than previously described, according to newly released documents from the National Transportation Safety Board.

A firefighter reported seeing "a white glow with radiant heat waves" but no flames out of the battery pack that caught fire Jan. 7 at Logan International Airport, according to an interim report by the NTSB released Thursday.

The NTSB has yet to figure out exactly what caused the shoe-boxed sized battery to overheat. The lithium ion battery is a much larger version of the battery that powers a laptop or cellphone.

Dreamliners worldwide have been grounded since a second battery incident led to an emergency landing in Japan nine days after the Boston fire.

U.S. Transportation Secretary Ray LaHood said in January he won't let the Dreamliners fly again until he's "1,000 percent sure" it's safe.

Boeing has been consulting with Ford Motor Co., General Motors Co., General Electric Co., United Technologies Corp. and others for battery solutions that will get its plane back in the air, Bloomberg News reported, citing five people with knowledge of the matter who are not authorized to speak publicly.

Boeing wants to insulate the battery and build a better box to contain any fire, according to published reports. Federal Aviation Administration officials are expected to make a decision soon on whether to approve a plan by Boeing to revamp the 787's lithium ion batteries to prevent or contain future fires.

Donald Sadoway, John F. Elliott Professor of Materials Chemistry at MIT, thinks that won't be enough to get the Dreamliner back in the sky.

"How do we insure that we don't get into a fire condition in the first place? And I haven't heard enough to give me comfort on that one," Sadoway said.

The fire that broke out in Boston was on an empty Japan Airlines Dreamliner after a nonstop flight from Tokyo, carrying 184 passengers.

The first firefighter to enter the plane reported seeing "a white glow about the size of a softball" through the smoke using his hand-held heat-imaging camera.

One of the firefighters responding to the fire reported that the "battery was hissing loudly and that liquid was flowing down the sides of the battery case," according to the NTSB report.

Another firefighter reported that he heard a "pop" sound and that smoke began "pouring out of" the electronic equipment bay, the NTSB said in the report.

In all, it took an hour and 40 minutes to extinguish the fire.

There are about 50 Dreamliners flying in the world, mostly for Japanese airlines, but also for Polish and Chilean carriers.

United is the only U.S. carrier flying the Boeing 787s, which have been touted as the planes of the future.